1. Field of the Invention
The invention relates generally to the formation of diols and polyols and formation of polyurethanes therefrom.
2. Description of the Prior Art
Epoxy compounds have been reacted with bisphenols to form high molecular weight polymers. These reactions typically result in solvent based resins that can then be cured with isocyanates.
Polyurethanes have been made from alcohols and isocyanates. These reactions may cure quickly, even at low temperatures. The polymers are generally flexible, tough, and have good adhesion, but have inferior chemical resistance in comparison to epoxy resins. Polyurethanes can suffer from cathodic disbondment, in general due to the nature of the diols, which are susceptible to hydrolysis under alkaline conditions. Polyether diols are also used, but suffer from high water pick-up. The traditional focus for polyurethanes has been for the decorative and automotive markets.
It is known that a polymer containing multiple hydroxyl groups can be cross-linked with isocyanates. However, the starting polymer may be a solid or have a high viscosity. The polymer may need to be dissolved in a solvent in order to perform the cross-linking. The solvent must then be removed from the system, typically by evaporation.
It is also known that polymers with terminal hydroxyl groups, such as poly(ethylene glycol), may also be cross-linked with an isocyanate. These polymers may also be a solid or have a high viscosity, requiring the use of a solvent.
It is also known that a low molecular weight polyol, such as low molecular weight poly(ethylene glycol) can be cross-linked with an isocyanate. These polyols suffer from the drawback that they are not compatible or soluble in the isocyanate.
Low molecular weigh esters and acrylics have been reacted with isocyanates to form thermosets. However, these polymers suffer from hydrolysis under alkaline conditions.
There is need for a polyol monomer that is compatible with isocyanates, such it can cross-link with a polyisocyanate without the need for solvent. The desirable system would have the chemical resistance of a polyepoxide and the curing and mechanical properties of a polyurethane.